This invention relates to a power source controller for an electronic control circuit having a main control circuit and a slave control circuit which is under the control of the main control circuit.
In order to control a complex control object including many functional parts, such a structure is adopted where a slave control circuit is provided for each of the functional parts and a central main control circuit controls the slave control circuits. By this control system, the overall control of the complex system is simplified, designing labor is reduced and thus cost of the total control system is minimized.
But the existence of plural control circuits brings about a shortcoming especially at the power-on and power-off of the overall system. When the slave control circuit is under normal control of the main control circuit, the functional part corresponding to the slave control circuit is controlled normally by the main control circuit via the slave control circuit. But when the power to the overall control system is initially turned on and the slave control circuit becomes operable before the main control circuit becomes operable, the slave control circuit may do an unexpected abnormal action over the corresponding functional part depending on the transient state of the slave control circuit because the slave control circuit is not reset and initialized by the main control circuit. Also, at the time of power turn-off of the overall control system, if the main control circuit becomes inoperable before the slave control circuit becomes inoperable, the slave control circuit may produce an unexpected action. Such phenomena tend to occur when the minimum operable voltage of the main control circuit is higher than that of the slave control circuit. A further related problem is that, when the control object includes a motor, the inertial rotation of the motor just after the power to the overall system is turned off can generate power with low voltage which will produce an unexpected operation of the slave control circuit without causing operation of the main control circuit.